Cold high-pressure metal vapor discharge lamps, such as sodium or halogen metal vapor high-pressure lamps, utilize igniter circuits in which pulses of electrical energy are superimposed above each other. Similar circuits can be used to re-ignite already warm lamps of this type. An auxiliary igniter capacitor is provided which is serially connected with a damping resistor. Small lamps, that is, lamps having power acceptance of up to about 400 W, can be operated without such damping resistors, if the inductance of the secondary of the pulse transformer is sufficient to limit the capacitor current, upon ignition of the lamp, to a suitable value.
An auxiliary series circuit can be connected by a relay contact, either manually operated or controlled by a starter or accessory unit when ignition is intended. Such igniter circuits are comparatively complex, expensive to manufacture, and are sensitive to temperature changes. They are subject to malfunction, and the power carrying terminals, especially, are sources of trouble.
Igniter circuits have been proposed in which, after ignition, further igniter pulses are suppressed by a semiconductor circuit. Such lamps, however, do not ignite reliably. This is particularly the case with respect to some lamps which have inherent ignition difficulties.
Igniter circuits have also been proposed in which audio frequency oscillations are generated to facilitate ignition--see, for example, German Pat. No. 1,589,306 (particularly FIGS. 3 and 4). These circuits have advantages, but have not been used commercially since some difficulties have been experienced. The circuits could not maintain the required operating range for reliable automatic ignition between about 160 and 198 V, especially in units made under mass production conditions. The phase position of the ignition pulses between 60.degree.-el and 90.degree.-el of the power frequency half-wave (50 or 60 Hz, as customarily used) required for reliable ignition could not be maintained.